As Ally Pally says, NVG's need some light to work.. .The light limits, for peace time, are about 2 millilux. This is about the amount of light coming from the sky on a clear night with no moon. A quarter moon gives about 7mlux. If there is no moon and the sky is overcast then there is obviously less light.

Over European type populated areas, this is not such a great problem as the light from houses, streetlights etc is reflected from the clouds(especially low cloud), and artificially boosts the light levels.

However, in remote areas, away from any domestic lighting and with an overcast sky it is VERY dark and you literally cannot see your hand in front of your face! NVGs just do not work in these situations.

Some of the more specialised US helos are equipped with FLIR(Forward Looking Infra Red). As these "see" minute changes in temperature, it's possible to fly using them where it's too dark for goggles. I think some may also have terrain following radar as well.

Unfortunately, we can't afford fancy stuff like that. <img src="mad.gif" border="0">

[ 24 February 2002: Message edited by: MightyGem ]</p>

Possibly the reason is the aircraft arnt NVG compatable. . .That is the cockpit and other aircraft lighting has to be modified so as to take out all white light.. .The slightest pinpoint of white light can severly effect the gogles..you can imagine unmodified annuciator lights or others lights comming on can effectively blind you.. .It's a major job to get airctaft NVG compatable.

Doogs <img src="smile.gif" border="0">

Av8R,. .I think you will find that the internal lighting of all RAF SH aircraft has been NVG compatible for some time now.

VfrPb,. .NVG only amplify existing lighting, as already stated (imagine them working a bit like a hearing aid. If there is no sound, then there is nothing to amplify into audible sound). Once in the mountains, the only light is from above rather than from all around as in more populated areas. If there is cloud cover and no moon then there is unlikely to be enough light to allow the gogs to do their stuff. The theoretical minimum light levels are great to bear in mind but the only effective way to assess the light levels is to put the gogs on and see if they work. Unfortunately this can put a crew at risk, and I can tell you from experience that there is nothing more frightening than when you lose visual reference on goggles at a critical moment. Aircraft can use IR searchlights for low and slow stuff but not for cruise flight. However, anyone with an IR gunsight can see the light source...

The FLIR kit isn't affected by low light levels as it works by converting heat into visible light.

I don't know anything specific about this incident but during the Indonesian conflict in the 60s in Borneo, a RAF single Pioneer pilot ran out of duty hours on his way back to Labuan and landed at a deserted airstrip and spent the night in his aircraft, no radio call to anyone. At 5 am I was invited to search for him and about 8 am, I heard his radio call for clearance to enter CTA. On asking why he spent the night in the bush, he stated war or no war, he could not exceed his duty hours!!. .PS I was not in the RAF!! <img src="eek.gif" border="0">[/LIST]<img src="rolleyes.gif" border="0"> <img src="rolleyes.gif" border="0">

Vfrpilotpb; where did you read about this originally?

This was well reported in the papers and on the radio.

Good morning , from the rainswept, quagmire called Lancashire, . .Harpooner,. .As Mighty Gem pointed out it was in many newspapers , I think I saw it in the "Times", but it was only a very small item , more of a attention grabber than the normal sort of Times reporting.. .I was under the impression that NVG would work in Zero lighting, but thanks to the ocean of knowledge that the Ppruners have I now know a little more.. .Thank you all.

My Regards. .Peter B :)

I know nothing of the origin of the post but, an observation, If I were comming from a training area of very few very tall mountains into an area such as Afganistan, with very tall mountains and very dark shadows (the shadow is an area of less light than the minimal you are flying in), I would be very hesitant to commit folks to flying in that environment with out lots of train-up time.

Have no idea if this was the case. Just an obsrvation.

Mighty and VFR; I seem to have missed such news recently as my floating grey hotel was out of range of the paperboy!

The truth of the matter is exactly as gem stated (light levels at Zero) you can practice in any environment you choose but faced with flight anywhere in black velvet bag conditions it is best to skip the odd job - least you end up with a belly full of sand, and no one will thank you for that.

Hello there, I saw this post, thought I would reply. As posted earlier, a good reason a NVG flight could not be made in a particular aircraft would be the cockpit not NVG compatable. As stated earlier would be the presence of white light. But red light is deffinatly worse with blue/green lighting prefered. And the NVG's are passive, they need some ambiant light in order to function. In absence of sufficient light a "pink" light is usually incorporated. The light is just a IR filter that is attached to the searchlight (ie UH60) and turns the passive system to active so the use is normally not considered "stealthy". . As for FLIR, dry/cool atmosphere yields the best results. Humidity seems to adversly affects thier performance.. . j

Hi think you will find tandemrotor's comments the most pertinent.

fyi the peacetime limit is 1 millilux. however i reckon allcrews who have operated will agree that there is no real definitive way of stating whether it is 1 millilux or less/more. in reality you lift and fly to the limits of you and your crew and if someone is not comfortable he will say so. lack of sufficient ambient light may have been a reason, but the RAF crews in theatre will be v exp in v low-light conditions and it would have to be practically nil for them to have aborted.

same with CDP and whilst it exists and is used in the RAF it is cited by others as an example of lack of flexibility. far from it, it is a system which is ideal for peacetime and durting ops is taken account of in the planning and if unexpected ops are anticipated, then that will form part of the pre-op planning to ensure the potential commitments can be met.

nvg helicopter
 

if you have NVG compatible helicopter,you must have special lights on helicopters(possition lights), some helos even have one's on rotor blades,so they are seen thrugh NVG glasses.

Didn't see the clip; however it's quite common.

Rock dust blown up by rotor blades may cause minor sparking as it interacts with the metal leading edge protection strips. This causes light which is amplified by the NVGs. At worst it can appear as a halo effect; not good as it makes the aircraft a clear target in the military sense.

We get the same effect to a lesser degree when landing at airfields where there is lose rock dust, our aircraft has titanium blade protection strips and the sparks are white and very visible without NVGs. I believe it is the granite used in many concrete mixes that causes the brightest sparking effect. Even though we don't operate our aircraft into dusty sites very often (UK mud instead), our leading edge strips are rough to the touch, caused by the resulting erosion.

The effect is astounding, and is even visible with the naked eye at times.

I believe the effect is piezoelectric, that is the production of energy when a crystal is squeezed or distorted. The sand paticles hit the blade and glow fiercely in the rebound. I don't think the metal on the blade is an important part of the equaton.

Try this: get into a very dark environment let your eyes dark adapt fully (20 minutes). Then hit a sugar cube with a hammer and watch the glow.

We ran a long thread on this a few months back.

Nick,

I tried that. Don't think I waited for my eyes to fully adjust. hit my thumb instead. No spark of light, but the air turned blue.

Colin :D

Nick,

Not discounting your piezo-electrics but I think the metal type of the leading edge protection does play a part in the effect. Perhaps there are two different effects / causes.

The S-76, the S-70 Blackhawk and the CH-53 all do it, especially in dusty conditions. Certainly on the S-76 you can see little white sparks bouncing off the underside of the blades with the naked eye even ground taxying at an airport but other types I have flown with stainless steel protection as opposed to titanium (flown into the same locations) don't seem to do it, even when shrouded in dust.

BTW, Have you seen the titanium studded knee-sliders that motorcyclists use to deliberately throw up a shower of white sparks on corners? Oh, sorry, you don't have corners in Florida do you? :D ;)

Anyone know what type of LE protection the Chinook has?

Can't wait till dark, got my 14lb lump hammer and box of cubes at the ready, not to forget the steel / titanium toecaps and eye protection. :eek:

Nothing to do with this really, but open carefully a self-seal envelope in the dark and the adhesive surfaces glow blue.

Snag is you can't read the letter:confused:

wintogreen lifesavers have a more noticeable effect, but thats because there are other things going on. Same idea initially, quickly break a crystal and you have an uneven distribution of charge. Electrons jump to equal the charge and in doing so emit a light whose color depends on the type of crystal, blue for sugar i think. Didn't know it was called piezoelectrics...learn something every day.

I saw the clip on cnn of a chinook landing through nvg...was very surprised how noticeable the effect was in Afghanistan. Seen it many times before both with and without NVGs, never that noticeable.

Unrelated: Best thing to see with NVG are comets. Hale Bopp light up the sky. That one with a Japanese name about a month ago wasn't visible unaided...awesome with goggles.

I've done quite a few jump seat trips in Chinooks while wearing gogs (NVGs) and the effect is very impressive (if a little disconcerting when you first become aware of it!)

Shy torque,

I learn each time I log onto pprune!

There are differences between rotor blades, but the Sikorsky family uses nickel strips, as does Boeing on their family, at least according to the web sites I found about 5 minutes ago. The Bell 430 uses nickel caps on its steel strips, so the actual impact surface is nickel, I think. Perhaps it is that way for the other newer design Bell baldes.

I must say that I don't know if the spark response different than other helos, I hope ppruners can help out. We can guess that CH-47, Bell 430 and H-60's are the same. Are they in reality?


Anyone with specific knowledge of different spark response (under goggles and not), with different helo types under the same operating environment?

This is interesting, isn't it?

Perhaps this effect should be taken into account during rotor blade design, as it obviously makes helis an easier night target.

There can't be many armies without night sights these days.

Blackhawk Halo
 

The Blackhawk main rotor blade has a fiberglass end cap. Only the Leading edge of the tip cap is Titainium, I was told on my NVG qual course that the lights you see are static discharge from the blade to the dust.
Funny Story, on that same course whilst conducting CCT's at Oakey (Queensland Aust) I eagerly warned my instructor of some inbound traffic that I had spotted far away, feeling quite smitten that I had picked up the moving pos'n lights of the said Acft out of the stars.
I was then informed by my hysterical QFI that the acft did not pose a threat to our operations, as it was in the holding pattern for a approach into Brisbane Int'l over 150kms away.
NVG's very effective..........:eek:

Bigdog1971,

I don't think that your instructor was right that the flashes we see are static electricity. The effect has been recorded several times that I have seen, and is seen as discrete sparks like glowing objects (a whole trail of them to be sure). Static disharge would be firey glow type stuff, like St Elmo's fire.

The blades on Black Hawk are well grounded to the head and fuselage, so charge will not build up unless the jumpers are misinstalled. I'll have our H-60 Chief Pilot communicate with the IP's at the Qual course to understand how they formed the opinion that static electricity is the cause.

Also, the Black Hawk does not have Titanium strips, they are nickle, even on the fiberglass tip caps. Looks like Ti, as it is a dull gray.

I guess the thing I'd like to understand is - Are the Black Hawk and Chinook different that other helos under the same conditions?

there was a huge post about this in late 2001 but I cannot seem to locate it for you. Will keep trying.

Nick,

I think that we "narrowed" down several factors on that last thread:

Airborne Dust density (related to downwash velocity, dust material and airspeed/height)
Dust material
Blade material
Air moisture - humidity

With all these variables, I think only a test pilot like youself could afford the time effort to find out if its different on different machines.:)

I have noticed that the Black Hawk has it heaps, with little dust required. The Chinook obviously has it, but it often seems to require more dust than the Black Hawk, the UH-1 has it but it seems to need heaps of dust. I have rarely, if ever, seen it with a B206. So in short - ******ed if I know!!

:D :D

Edited to add the previous thread:
http://www.pprune.org/forums/showthr...threadid=18985

That is the link (not good with these). other way to find it is to search in rotorheads for Icing - and other wx nasties

If you are brave enough to read through the pages, there is a lot of info hidden amongst the banter.

This is an about face for myself. The previous thread had someone wondering whether this effect lit up helicopters enough so that someone on NVG could find a helicopter that was trying to hide close to the ground. I went with the consensus and thought that there was not enough light to be a problem. I'm now reconsidering.

Two things changed my mind. One was the CNN footage. I was amazed how bright it was. Of course, the cameraman knew where the helicopter was, and was zoomed in on him, so at first I didn't think it was a problem. Then I remembered SAR Coad.

SAR Coad was a mission I was on right after I converted to NVGs. Two guys in a Cessna crashed in highly mountainous area in April. Aircraft was found and two sets of footprints walking downhill away from the crash site. Two problems with this. One, they weren't dressed for it, and two they were headed for a river. That survival thing about following rivers doesn't work in many mountainous areas. The rivers are too carved out and thus too steep for easy travelling. Anyhow, nightfall approaching, their injuries still undetermined and hypothermia is a real possibility.

We got on scene at dusk, donned NVGs enroute, and started searching. One crewmember noticed an unusual flashing light about three miles from our location. Investigating, we found the two survivors and pulled them out with only scratches, bruises, and a little bit cold.

Good story, huh? What does this have to do with blade sparks? The flashing light was a Bic lighter that had no fluid in it. He wasn't signalling us, just trying to get the lighter lit to start a signal fire. We saw the spark of the flint from about three miles through tall trees.

Makes me think that this blade spark show might just provide enough illumination for someone overhead to spot you.

Night Vision Goggles
 

I saw an advertisement by Bell offering a course in the use of NVG's. I'm not thinking doing it, but it got me wondering how they work.
I know the AAC use them - can any mil pilots explain how they work etc.
Bell say low level, middle-of-the-dark-night missions have become routine with NVG's, you 'can literally see in the dark', and night ops can be completed 'nearly as normally' as during the day.
True or advertising blurb?

What are the limitations?

Virgin, a detailed reply to your question would take up most of the pprune mainframe memory so i'll try to keep it short!
NVGs work on the image intensification principle, ie, amplifying light energy. Within each tube is a photocathode which receives the incoming light radiation and after impact, a stream of electrons accelerate away from the photocathode and strike a phosphor screen. The power supply creates an electrical field which produces the means of acceleration. Essentially, the phosphor screen emits light in proportion to the amount of electrons that strike it. When voltage is applied, the electrons brighten creating an image that can be seen.

The current generation of NVGs produce superior amplification of somewhere in the region of 3000 times from the ambient conditions. Good enough for low level flying in low light level conditions of perhaps less than 1 mililux.
Limitations:
NVG performance is directly related to the ambient conditions. they will let you down if there is not enough light!
Bright lights will close down, or whiteout the goggles.
Fields of view are in the region of 40 degs so head movement is important to substitute peripheral vision.
Depth perception can be difficult.
No colour, a green image is tiring.
Wires are difficult to see.

Will that do for now?

A basic page, but fufills your question on how they function.

http://www.morovision.com/howset.html

Virgin -
NVG flight has been the norm for military hels for years now (I believe that they were first used by the French helicopter crews in Vietnam) to the extent that non NVG flight is known as 'reversionary' night flying. It is pretty much true that, if you are a REGULAR user, you can do most things visually at night on goggles. There is no secret to the technology, it is just two TV screens placed in front of your eyes that have had the electrons in the tubes amplified by about a thousand times. In terms of limitations they are bloody heavy, they 'bloom' out if exposed to too much light and they have poor peripheral vision leading to a lack of near field visual clues at low speed/height. The biggest limitation of all however is that a thousand times **** all is still **** all and therefore they will not help you on a dark night over the sea/desert or in the mountains.

:cool:

Night Vision Goggles
 

NVG are excellent aids but must be used wisely and with caution. The number of NVG related accidents amplify this adequately.

I had the great fortune whilst flying low level, solo, on goggles, over the sea from Anglesea to Carlisle, to see the "Northern Lights" on the goggles but not with the naked eye - very spectacular!

I would not go anywhere without them but am very aware of their limitations and mine.

A very wise pilot once asked me to consider what the doctor would say at my next aircrew medical if I told him that my vision was limited to a 40 deg field in varying shades of green...

hh

I believe Devon & Cornwall Police use NVG in their 117? Anyone any knowledge of this?

The D&C BK117 is I believe the only aircraft currently CAA approved for night operations. The Alan Mann Group did the work.

slightly off topic...
 

... but a policeman was sitting beside the A1M (a local motorway) late at night was surprised when two cars flashed by at considerably more than 100mph without lights on a dark night on an empty, unlit road.

Turned out it was local heli pilots from a military base using NVGs to drive their cars in "stealth" mode.

could be an urban myth, but heard it from a usually reliable source.

I've used Litton M949 Night Vision Goggles with ANVIS white LED-based auxiliary lighting system installed in a 206BIII at Bell. They're now using that combination for the factory NVG course.
I thought it was pretty good, but didn't use it on a live mission.
Anybody else used that gear?
Anything out there better?

Main points been highlighted, heavy, poor (no) periph vision, poor depth.

I have had difficulty getting the right focal plane when using them as well - admittedly they were cheap ex-Russian stock, not the modern 3rd gen US stuff - does anyone have any experience of how to look at the instruments (close up) and then at a long distance?

And they bleach badly with a Nite-Sun!!

By the way, does the D&C 117 fly with two pilots, or just one at night?

Anton

NVG photograph through one lense:
 

This will take a while but is worth the wait:



http://www.artistic.flyer.co.uk/nvg.jpg

Anton,

You can't look at the instruments through the goggles. The goggles are focused to infinity, and are used for looking outside the cockpit. It is best to set them about 1 inch away from your eyes, and you look under them with the mark 1 eyeball to look at your instruments. Of course, you need NVG compatible lighting in the cockpit (blue), or the glare will prevent you from seeing anything through the goggles.

Now I was always taught that it is red light that affects night vision the least, so why do all NVG's produce a green image ?

Just an idle thought

Cheers all

NVGs are worth the effort and expense. They make night flying without them downright frightening.
They are heavy at first, however if used correctly, with a good mounting system and the battery pack fitted to the rear of the helmet with a weight bag (max 450gm) you should not have too many problems. Weight bags are a personal option where I come from. If you do it properly you probably won't need one. I don't use one anymore.
The key is to ensure your helmet is a nice snug fit. If you cannot wear your helmet for hours without getting 'hotspots' and general discomfort then sort that out first. Wearing NVGs without a helmet is fraught with frustration and discomfort!
As for the rest of fit, the manufacturer's handbook should be ample advice. Other posts on this thread have covered the salient points. Ensure though that they are focused to infinity.
Flying with NVGs is a perishable skill. Conversely, the more you do it, the better you get. IMHO, to maintain your skills at tip top condition, at least 5hrs/mth. That is the ABSOLUTE minimum. 10hrs/mth would be more realistic. The course would likely be 10-20hrs of ICUS type supervision.
Using NVG with 'white light' eg a NiteSun, is not good. Avoid it as their resolution falls away rapidly. It is better to have an Infra-Red filter over a searchlight of about 250W. The later model NVGs don't flare out too badly around external white light, and work well for urban ops.
Many of the civil authorities appear to have a great fear of legalising NVG, however I believe that those fears are only partially founded.
NVGs are one of the best things around for night ops, have no doubt.

3D, the green monochromatic colour is due to the type of phophor screen used within the tube. A usual after effect when using nvg for extended periods is 'brown eye'. This is evident when you remove the nvg and look unaided. This afterimage is called chromatic adaptation and goes after a while, normally as you get to the bar!